Studies from the “UWL Helgoland” on the macrobenthic fauna of rocks and boulders in Lübeck Bay (western Baltic Sea)

Abstract

During a fortnight's saturation mission with the Underwater Laboratory (UWL) “Helgoland” in May and June 1975, samples of the macrobenthic fauna of rocks and boulders at 15 m depth in the Lübeck Bay were collected from the same area as in October 1974, using a diver-operated suction sampler. Salinity varied from 11.1‰ to 15.0‰ S and water temperature from 7.5° C to 11.5° C. Visibility was usually about 3 to 4 m. On average, 10.449 individuals/m² were recorded in 1975 compared to 30.474 individuals/m² in 1974. Two species, the ascidianDendrodoa grossularia and the polychaetePolydora ciliata account for 90.8% of the total number of individuals sampled. Five species (Dendrodoa grossularia, Nereimyra punctata, Neoamphitrite figulus, Asterias rubens, Facelina drummondi) were significantly less abundant than in 1974, while two species and one group of species (Anaitides maculata, Corophium bonelli, Nemertini indet.) were more abundant in 1975. As in 1974, the angle of inclination of the substrate showed no relationship with species composition. In 1974, four motile benthic invertebrates,Nereimyra punctata, Idothea baltica, Diastylis rathkei, andFacelina drummondi were observed swarming. In 1975, onlyI. baltica was observed swarming and the individuals seemed to be less active than in 1974, perhaps related to the lower water temperatures recorded in May and June 1975 compared to those in October 1974.